Okay, since Windows 10 doesn't normally shut down fully, hold down the Windows and R keys together to get the Run dialogue box open, type in cmd, and then hit Enter. Within the Command Prompt dialogue box, type in the following and then hit Enter: shutdown /s /t 0 (that's a zero at the end). Note: this will turn off your PC, so ensure you've saved all your files and exited applications properly.
Once the PC is shut down fully, hit the Power button and - as soon as you do that - start mashing the F2 key repeatedly to get to setup.